Many cancers are caused by the aberrant activity of mutant versions of normal proteins, which are critically dependent on the 'molecular chaperone' Hsp90 for folding. Hsp90 does not act alone, but associates with the proteins Hsp90, Hsp70, HOP and CHIP in multi-protein assemblies. These associations are mediated by motifs called TPRs. The goal of this proposal is to develop an atomic force microscope (AFM) imaging-based assay that will allow a detailed study of the assembly of these nano-scale complexes. Using biotinylated HOP and streptavidin surfaces, Hsp90-HOP-Hsp70 assemblies will be studied and their formation monitored in situ and in real time. In addition, using the same AFM-based assay, the role of CHIP and the nature of its interaction with the Hsp90-HOP-Hsp70 assembly will be elucidated. Finally, this assay will be used to understand the effects of tighter binding TPRs and small molecules, which are capable of inhibiting Hsp90- HOP-Hsp70 formation. These novel studies will allow a new level of understanding of these nano-scale processes and assemblies. They have direct relevance to cancer, because inhibition of Hsp90 activity is a proven route to anti-cancer therapeutics.